As various electronic devices such as a personal computer, a digital camera, a mobile phone, etc., progress toward miniaturization and high performances, demands for further miniaturization, thinning and high density are rapidly required in a semiconductor device. Therefore, it has been desired to develop a photosensitive insulating material which can cope with increase in a substrate area for improvement in productivity, and, can form a fine film with high aspect ratio on a substrate in the high density mounting technology such as a chip size package, a chip scale package (CSP) and three-dimensional lamination.
In the high density mounting technology like a three-dimensional lamination, as a photosensitive insulating material which is able to subjecting to patterning on the substrate, a polyimide film has been used as a protective film or an insulating layer, and its insulating property, mechanical strength, adhesiveness to the substrate, etc., are continuously attracted attention, and development thereof is vigorous even now.
As a photosensitive polyimide-based material, a material utilizing a polyamic acid which is a precursor of polyimide, for example, a material in which a photosensitive group is introduced into a carboxyl group of the polyamic acid by an ester bond (Patent document 1, Patent document 2) has conventionally been proposed. However, in these proposals, imidation treatment at a high temperature exceeding 300° C. is indispensable in order to obtain a target polyimide film after formation of a patterned film, so that it involved the problems that an underlying substrate is restricted to endure this high temperature and the copper of the wiring is oxidized.
As an improvement thereof, it has been proposed a photosensitive polyimide using an already imidated solvent-soluble resin for the purpose of lowering the post-curing temperature (Patent document 3, Patent document 4). In a negative photosensitive resin composition using a polyimide described in Patent document 3, development using N-methyl-2-pyrrolidone (NMP) is carried out in patterning, but there is not described in Patent document 3 about specific description on resolution in the patterning.
On the other hand, the photosensitive resin composition proposed in Patent document 4 uses an already imidated base resin which has been constructed in view of low temperature curing. The solvent of the composition is cyclopentanone, and an alkaline aqueous solution is used in developing. However, improvement in resolution has yet been required. That is, patterning using a photosensitive resin composition described in Patent document 4 has been carried out with an extremely thin film, and a pattern size to be resolved is large. This lack of resolution performance is due to poor solubility of the polyimide resin, which is the base resin disclosed in Patent Document 4, in an alkaline aqueous solution used for a developer. It is a key for improving the resolution performance in patterning to heighten solubility of a resin in a developer.
In fact, as the resolution performance of the photosensitive insulating material in the high density mounting technology such as the three-dimensional lamination which is required in recent years, the aspect ratio (film thickness at the time of finishing (or height of pattern)/pattern dimension) of the formed pattern is required to be 1 or more and 2 or so. That is, when the desired film thickness at the time of finishing or the height of the pattern is 10 μm, a pattern with a dimension of 10 μm or less or a dimension of near 5 μm must be formed.
By the way, in Patent document 5, there is an example of a patterning process of a photosensitive resin composition using a material utilizing a polyamic acid which is a precursor of a polyimide, for example, a resin in which an ester bond is introduced into the carboxyl group of the polyamic acid, where, after forming a film, heating to be applied to obtain an objective polyimide film is carried out at a relatively low temperature of 250° C. While an organic solvent of N-methyl-2-pyrrolidone is used in the development, there is no disclosure about specific resolution in this Patent document.
With regard to patterning of the negative photosensitive resin composition using a precursor of a polyimide, there is Patent document 6. In the development of the patterning of the photosensitive resin composition, cyclopentanone is used. With regard to resolution performance, it has been specifically disclosed, and disclosed that an aspect ratio of 1 or more can be accomplished. However, this aspect ratio does not represent a ratio of a film thickness at the time of finishing or a height of the pattern to a dimension of the pattern, but a ratio of a film thickness after coating and drying to a dimension, so that this resolution performance is not a practical value, and an improvement is required. It is preferred to use a versatile organic solvent such as cyclopentanone as a developer, but when an organic solvent is used, the defect that a pattern profile immediately after the development likely becomes an overhang profile sometimes occurs due to swelling of the film during the development.
Further, with regard to patterning of the negative photosensitive resin composition using a precursor of a polyimide, there is Patent document 7. The developer in the patterning of the photosensitive resin composition is an alkaline aqueous solution. In this patterning process, solubility to the alkaline aqueous solution of the developer is improved by introducing an acid group into the resin of the polyimide precursor, i.e., an alkali-soluble group such as a carboxyl group, patterning by the development using the alkaline aqueous solution is carried out. The development using the alkaline aqueous solution has advantages that it difficulty causes swelling, a pattern profile becomes good and resolution performance is also improved. However, when an alkali-soluble group which enables the development using the alkaline aqueous solution is introduced into the resin, whereas it works dominantly in improving the resolution, it cannot avoid the problem that resistance to an extremely strong alkaline peeling liquid used for peeling the resist pattern for plating used in metal wiring process after curing is impaired. In order to form an excellent protective insulating film, it is necessary to completely seal the alkali-soluble groups present onto the resin or completely remove them from the system.
Thus, accompanied by high densification and high integration of the chips, miniaturization of the pattern in the rewiring technology of the insulating protective film is expected to be promoted more and more in the future, so that in the photosensitive resin composition using a polymer having a polyimide precursor structural unit, a composition which can realize high resolution without impairing excellent characteristics of a pattern of the polyimide obtained by heating and mechanical strength, adhesiveness, etc., of the protective film has been strongly desired.
It has been also strongly desired that the insulating protective film subjected to patterning and curing has heat resistance in various processes and resistance to various chemicals to be used.
That is, rapid development of the photosensitive resin composition having all of these features without lacking any of these has been desired.